1. Field of the Invention
The present invention relates to a print gap adjusting device to be used in a serial printer.
2. Description of the Related Art
FIG. 8 shows an exemplary print gap adjusting device in the related art. In FIG. 8, reference numeral 1 denotes a platen. A carrier shaft 2 parallel to the platen 1 is movably supported at both ends to opposed side plates (not shown) in such a manner as to be biased toward the platen 1 by a spring 3 and be moved toward or away from the platen 1. A carrier 4 is slidably supported on the carrier shaft 2. The carrier 4 is reciprocatively driven along an axial direction of the platen 1 by a carrier driving portion (not shown). A dot printer head 5 as a print head and a sheet holder 6 are mounted on the carrier 4. The sheet holder 6 is interposed between the dot printer head 5 and the platen 1 so as to be slightly spaced from a front surface of the dot printer head 5, thus functioning to hold a sheet of paper 7 fed onto the platen 1.
Accordingly, the carrier shaft 2, the carrier 4, the dot printer head 5, and the sheet holder 6 are advanced toward the platen 1 by a biasing force of the spring 3 as a driving force until the sheet holder 6 comes into contact with the paper 7 on the platen 1. In this condition, a space between the platen 1 and the sheet holder 6 is equal to the thickness of the paper 7. Further, a space between the sheet holder 6 and the front surface of the dot printer head 5 is fixed. Accordingly, a fixed print head is defined between the surface of the paper 7 and the front surface of the dot printer head 5 irrespective of the thickness of the paper 7.
The above-mentioned device in the related art has the following problem. In such a conventional serial printer as shown in FIG. 8, the dot printer head 5 and the sheet holder 6 both related by the carrier 4 are moved along the platen 1. Accordingly, there is a possibility that the paper 7 held on the platen 1 by the sheet holder 6 may be rubbed by the front surface of the dot printer head 5. In other words, when the paper 7 has a thickness equal to or greater than a given value (e.g., 0.35 mm), the above problem hardly occurs because the thick paper has a stiffness to some extent. However, when the paper 7 has a thickness less than the given value, the above problem readily occurs because the thin paper is less stiff. That is, the thin paper is readily bent or wrinkled. As a result, the paper 7 is rubbed by the front surface of the dot printer head 5, causing damage to the paper 7 such as cutting or breaking of the paper 7.
Although not shown, prior inventions intended to adjust the print gap according to the paper are known from Japanese Patent Laid-open Nos. Hei 2-113979, 4-31073, and 4-31074, for example. However, these inventions are not intended to solve the above problem.